1. Field of the Invention
The present invention relates to a magnetic recording medium. More particularly, it relates to a magnetic recording medium for master.
2. Description of the Prior Art
In a magnetic record reprinting method which is well-known as a contact reprinting method, original records are maintained in a master tape or sheet having a coercive force higher than the coercive force of a magnetic tape or sheet used for magnetic reprint and the master tape or sheet is brought into contact with a magnetic tape or sheet (slave) on the magnetic layers and alternative magnetic field which is remarkably higher than the coercive force of the magnetic tape or sheet is applied to perform the reprint from the master tape or sheet to the magnetic tape or sheet. In the operation, the following conditions are required; (a) the original record in the master tape or sheet is not affected by the magnetic field; (b) the reprinted record should be a faithful copy for the original record, tone qualities of the master tape or sheet and the reprinted tape or sheet are excellent. These requirements are further severe when the contact reprinting method is applied for a high density recording especially for a video tape or sheet. In usual, such purposes may be attained when the coercive force of the master tape or sheet is 2.5 times or higher than the coercive force of the slave tape or sheet. The coercive force for the high density recording such as the video tape should be about 700 Oe. Therefore, the coercive force of the master tape or sheet should be 1800 OE or higher. Moreover, the magnetic powder for the master tape or sheet should be selected from ones having excellent magnetic characteristics having low noise and high S/N ratio. When the master tape or sheet is used as the master for reprinting the high density record (shortwave record), it is important to consider the close contact of the master tape or sheet with the slave tape or sheet. If the surface smoothness of the master tape or sheet is not good, the spacing loss is large in the condition contacting with the slave tape or sheet and the reprinted degree is locally fluctuated even though the slave tape or sheet having excellent surface smoothness is used. Therefore, the master tape or sheet should have as indispensable conditions that the coercive force Hc should be 1800 Oe or higher and the surface smoothness should be superior to the surface smoothness of the slave tape or sheet and the noise is low and the S/N ratio is high to be at least 40 dB.